This invention relates to an apparatus for the production of a substantially nonturbulent stream of cooling gas for quenching one or more synthetic filaments produced by a melt spinning process.
In a typical melt spinning process, one or more filaments is extruded from one or more spinnerettes and passed into a quenching chamber. The quenching chamber comprises one or more walls, one of which is a diffuser separating the quenching chamber from an adjoining plenum chamber which is in communication with a cooling gas supply system. The synthetic polymer extruding from the spinnerette is a viscous liquid at an elevated temperature. Cooling of this liquid takes place in the quenching chamber where a cooling gas, which is usually air, is contacted with the filaments. The cooling gas enters the quenching chamber from the plenum chamber through the diffuser in a direction substantially perpendicular to the filaments. The filaments pass through the quenching chamber in a direction substantially parallel to the diffuser separating the plenum chamber from the quenching chamber. The use of the diffuser is necessary to reduce cooling gas turbulence; filaments are highly vulnerable to cooling gas turbulence since they are in the liquid phase at entry into the quenching chamber. Turbulence in the cooling gas stream detracts from the uniformity of the filaments.
Today, the demand is for higher yields at higher throughput rates while maintaining, preferably improving, yarn properties. One method of obtaining greater capacity is to increase the number of spinnerette extrusion orifices, resulting in a corresponding increase in the number of extruded filaments. Existing space limitations often dictate the maximum spinnerette plate size, and an increase in the number of extrusion orifices therethrough results in decreased extrusion orifice spacing. Faster yarn speeds coupled with decreased distances between spun filaments, causes undesirable crowding of the filaments, frequently with interfilament collisions, in the quenching zone. As a consequence, improving the stability of the threadline and improving yarn uniformity are very important. To realize these objectives, there must be better control of the quench gas flow rate and more uniform distribution of cooling gas across the diffuser and within the quench cabinet.
The diffuser has been the primary means of reducing turbulence in the cooling gas stream. There are a variety of diffusers in the prior art; these include screens, porous foam, perforated metal plates, sintered metal, metallic wool, and sandwiches of mesh screens, to name a few. The design of the diffuser is critical as it determines the velocity profile of the cooling gas in the quenching chamber. In quench cabinets designed such that the cooling gas is supplied to the diffuser other than laterally thereto, the incoming gas must be turned through an angle in the plenum chamber so as to pass through the diffuser into the quenching chamber. For example, a typical cross flow quench cabinet with the gas intake at the rear of its base must turn the incoming gas through a right angle so that it can pass laterally through the diffuser. This is critical because the design of the gas intake plenum chamber determines the velocity distribution of gas supply to the diffuser pack which, as mentioned previously, determines the velocity profile of the cooling gas in the quenching chamber. Turning vanes of the inclined ladder type have been used in the plenum chamber to turn the cooling gas through this angle. However, the incoming gas tends to be deflected at an angle similar to the angle of incidence, resulting in a higher velocity region over the lower portion of the plenum chamber between the turning vane and the diffuser. As a consequence, the gas flow supplied to the diffuser is very uneven, and the diffuser must be extremely efficient to smooth out the velocity profile of the cooling gas for contact with the melt extruded filaments. Without the turning vane, cooling gas is randomly distributed in the plenum chamber and again, the velocity profile of gas supply to the diffuser pack is uneven.
In conventional quenching chambers having substantially cross flow of the cooling gas therethrough, the cooling rate decreases as the filaments descend through the quenching chamber. It is therefore desirable to have a quench system which is flexible enough to allow different cooling gas rates to be supplied to varying sections of the quenching chamber. FIGS. 2 and 3 of U.S. Pat. No. 2,273,105 depict a quench system having a plurality of sections, to each of which a cooling medium is separately supplied and which are separated by partitioning means. The velocities of the cooling mediums being supplied to these sections can be varied independently. The chief disadvantage of this patented apparatus stems from the straight-line jetting action of the air on entering the plenum chamber, which jetting action tends to cause uneven velocity distribution of the air downstream of the diffuser. U.S. Pat. No. 3,274,644 provides a quenching chamber comprising essentially vertical inlet and outlet panels for allowing a gaseous cooling medium to pass through the chamber, and means for passing the extruded filaments vertically downwards through the chamber. Each of the inlet and outlet panels comprises a plurality of adjacent, horizontally disposed sections, and each of the sections contains means for individually regulating the stream of the gaseous cooling medium passing through the section. Unfortunately, regulating the apparatus of this patent is relatively difficult and unduly complicated for commercial operation.
The apparatus of the present invention essentially eliminates all of the aforementioned problems and yields yarns of high quality at high rates. The internal parts are designed so as to allow different gas rates to be supplied to the upper and lower zones of the quench cabinet with, simultaneously, turbulence being reduced and the velocity profile of the cooling gas at the upstream face of the diffuser being smoothed for passage therethrough.